title: Inhibition of gap junctional intercellular communication by tumor promoters in connexin43 and connexin32-expressing liver cells: cell specificity and role of protein kinase C.
abstract: In this study, we investigated whether the tumor promoters, 12-O-tetradecanoylphorbol-13-acetate (TPA), phenobarbital (PB), and 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), inhibited gap junctional intercellular communication (GJIC) in a cell-specific or connexin-specific manner and whether protein kinase C was involved. To do this, we used highly communicating WB-F344 rat liver epithelial cells, which express connexin43 as their predominant gap junction protein, WB-aB1 cells, which are a GJIC-incompetent mutant line of WB-F344 cells and that express connexin43, WB-a/32-10 cells, which are a highly communicating derivative of WB-aB1 cells generated by stable transduction with a connexin32 retroviral expression vector, and primary cultured rat hepatocytes, which express conexin32 predominantly. Treatment of WB-F344 and WB-a/32-10 cells, but not hepatocytes, with TPA inhibited GJIC (assayed by Lucifer Yellow dye microinjection). This inhibition involved protein kinase C because (i) inhibition was prevented by co-treatment of the cells with a specific protein kinase C inhibitor, bis-indolylmaleimide, and (ii) treatment with TPA for 24 h had no effect on dye-coupling in agreement with the downregulation of protein kinase C. TPA also caused the internalization of Cx43-containing gap junctions and the formation of a hyperphosphorylated form of Cx43, Cx43-P3, in WB-F344 cells only, but TPA had no effect on Cx32-containing gap junctions or protein mobility. In contrast, PB inhibited GJIC only in hepatocytes and DDT inhibited GJIC in all three types of cells; bis-indolylmaleimide did not block the effects of either agent. These results indicate that the inhibitory actions of TPA and PB on GJIC are cell-specific rather than connexin-specific and that TPA inhibits connexin43 and connexin32-mediated GJIC through a protein kinase C-dependent mechanism.
authors.affiliation: Department of Pathology, Medical College of Ohio, Toledo 43699, USA.
authors.forename: P
authors.initials: P
authors.lastname: Ren
authors.forename: P P
authors.initials: PP
authors.lastname: Mehta
authors.forename: R J
authors.initials: RJ
authors.lastname: Ruch
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000494:pharmacology*; D002450:Cell Communication / Q000187:drug effects*; D002478:Cells, Cultured; D018031:Connexin 43 / Q000096:biosynthesis* / Q000502:physiology; D017630:Connexins / Q000096:biosynthesis* / Q000502:physiology; D003634:DDT / Q000494:pharmacology*; D004789:Enzyme Activation; D017629:Gap Junctions / Q000187:drug effects / Q000502:physiology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010634:Phenobarbital / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011916:Rats, Inbred F344; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014158:Transcription, Genetic; D000097002:Gap Junction beta-1 Protein
chemical_list: D002273:Carcinogens; D018031:Connexin 43; D017630:Connexins; D003634:DDT; D010634:Phenobarbital; D011493:Protein Kinase C; D012333:RNA, Messenger; D013755:Tetradecanoylphorbol Acetate; D000097002:Gap Junction beta-1 Protein